The trend in the field of catalytic cracking, and particularly in fluid catalytic cracking (FCC), has been to employ high activity catalysts and operate the catalytic cracking process at increasing temperature regimes; for example, at temperatures in the range of about 525.degree. C. to about 555.degree. C. This has necessitated the rapid separation of catalyst from hydrocarbons being converted in the fluid catalytic cracking reactor in order to reduce the contact time of the catalyst with the hydrocarbon products, thereby preventing undesirable excessive cracking of the products in the contacting zone with the concomitant deposition of carbon on the catalyst particles. One method employed in reducing the contact time of the catalyst with the hydrocarbon products involves transferring suspended catalyst and hydrocarbon upwardly through a riser conversion zone (FCC cracking zones) and feeding the catalyst particles suspended in the gaseous phase into a cyclone system attached to the riser. Examples of such systems can be found in U.S. Pat. No. 4,778,660, U.S. Pat. No. 4,606,814, U.S. Pat. No. 4,909,993, U.S. Pat. No. 4,654,060, U.S. Pat. No. 4,502,947, U.S. Pat. No. 4,737,346 and U.S. Pat. No. 4,623,446.
Alternatively, systems have been proposed in which the riser and cyclone are open to a dilute phase zone in the FCC vessel. Examples of this type of system include U.S. Pat. No. 3,152,066, U.S. Pat. No. 4,394,349, U.S. Pat. No. 4,446,107 and U.S. Pat. No. 4,946,656.
Notwithstanding the many techniques employed for separating FCC products from catalyst, a need continues to exist for developing new and more efficient systems for decreasing the contact time of hydrocarbon vapor products and catalyst in fluid catalytic cracking vessels. This need is particularly important as the industry shifts toward using heavier feedstocks in process units running at higher temperatures and employing more active catalysts.
An object of the present invention is to provide a process and apparatus to reduce residence time of hydrocarbon conversion products in a fluid catalytic cracking reactor vessel.
It is a further object of the present invention to use the energy of the riser discharge or, in the alternative, the riser cyclone discharge, to actively assist in removing the vapor from the dilute phase in the reactor vessel.
Other objects of the present invention will become apparent upon reading the "Detailed Description of the Invention".